Thermal protrusion reduction in magnet heads by utilizing heat sink layers

ABSTRACT

A magnetic read/write head and slider assembly and method for forming said magnetic read/write head and slider assembly, wherein said assembly has improved heat spreading and dissipation properties and exhibits significantly reduced thermal protrusion during operation. The method consists of the formation of a heat sink layer on a portion of either the upper pole yoke or the lower magnetic pole of the writer.

CONTINUATION-IN-PART

[0001] This Application is a Continuation-In-Part of Docket No. HT 01-017, application Ser. No. ______ Filing Date Oct. 5, 2001.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] This invention relates generally to the fabrication of merged magnetic read/write heads and slider assemblies and, more particularly, to the fabrication of such a head and slider assembly with improved heat spreading and dissipation characteristics to eliminate problems associated with thermal expansion and protrusion of head elements during operation.

[0004] 2. Description of the Related Art

[0005] A merged magnetic read/write head and slider assembly consists essentially of a magnetoresistive read sensor element formed on the pole pieces of an inductively magnetized write element and mounted within, or fabricated as an integral part of, a slider assembly that physically and electrically connects the head to an actuator arm. The read/write head is subjected to complex thermal stresses during its normal operation due to the buildup of thermal energy from Joule heating in its read and write stages (sensing current in the read element and write current in the write coil). The heat dissipation properties of the read/write head are limited by the thermal conductivity of the protective overcoat material (typically sputtered alumina) that covers the head. Since alumina is a relatively poor conductor of heat, a temperature buildup occurs in both the head and the overcoat as the overcoat is unable to eliminate the heat produced in the head with sufficient rapidity.

[0006]FIGS. 1 and 2 show two schematic views of a read/write head and slider assembly. FIG. 1 shows a cross-section of the head attached at (15) to the actuator arm (30). Details include the overcoat (2), the upper (6) and lower (4) pole-pieces and the insulation imbedded coil structure (5) that inductively activates them. The read element (8) is generally formed beneath the lower pole piece (4) which then also serves as an upper shield for the read head. The air-bearing surface of the head, at which the read element is positioned, is indicated as (1) and the dimensional direction “x” is also shown. The trailing end, containing the connecting pads (only (10) is shown), is indicated as (14). FIG. 2 is a schematic drawing showing the trailing end surface (14) of the read/write head assembly where it attaches to external wiring (shown as (13) in FIG. 1) along the actuator arm. The dimension “z” on the drawing would be coming out of the plane of the drawing in FIG. 1. FIG. 2 also shows four gold pads (16, 18, 20, 10) which make the electrical connections to the head assembly. Two of the pads (10 & 20) provide the sense current for the read sensor through internal wiring (9), while the remaining pads (18, 16) provide the coil current for the write head through wires (19). These figures will also be discussed below in the context of the description of the first of the preferred embodiments.

[0007] Seagle (U.S. Pat. No. 5,936,811) provides a slider assembly similar to that in FIGS. 1 & 2 in which the current carrying leads are disposed in a manner that eliminates the need for vias passing through the insulating layers and shield layers to allow the electrical activation of the read and write sensors.

[0008] Chang et al. (U.S. Pat. No. 6,158,107) provide a merged read/write head in which the pole tips of the write head are more advantageously defined by use of a self-alignment formation process and show the use of a substantial overcoat in the head formation.

[0009] Maries et al. (U.S. Pat. No. 3,770,403) discloses a magnetic head assembly in which the read/write circuit portions of the assembly are formed on a chip and bonded to head assembly by a glass-ceramic material whose coefficient of expansion matches the coefficient of expansion of the parts to be joined. Another feature of this structure is that the method of mounting the head assembly on the support arm allows the air flow past the assembly to act as a coolant for the circuit chip and also allows the thermal conductivity of the metal structure of the arm to act as a heat sink for the circuit chip.

[0010] Phipps et al. (U.S. Pat. No. 5,757,590) deals with the problem of electrostatic charge buildup on read/write heads, which is another problem associated with rapid relative movement between the head and the recording medium. Phipps provides a fusible link element connected across the existing terminal pads of the head to discharge the unwanted buildup.

[0011] Wang et al. (U.S. Pat. No. 6,130,863) show the use of a magnetic coil and slider assembly even in the field of magneto-optical storage systems.

[0012] Han et al. (U.S. Pat. No. 6,103,136) shows a magnetoresistive read head that typifies those found in the merged read/write heads referred to in the present invention.

[0013] Ibaraki et al. (JP5266428A2) provides a thin film magnetic head with star-shaped metallic patterns formed on a protective overcoat to dissipate Joule heating.

[0014] With the exception of Ibaraki et al., none of the prior art cited deals with the significant problem of heat buildup in head elements such as write coils, magnetic pole pieces, overcoat regions and magnetoresistive sensing formations. This heat buildup is not only damaging to the performance of the elements, but differential thermal expansion causes protrusion of elements relative to each other and relative to the air bearing surface, which protrusion can cause damage to the rapidly moving storage medium. Ibaraki teaches a star-shaped conductor pattern disposed on the lateral edges of the protective overcoat on a magnetic head. The pattern is not placed directly over the heat producing elements as it is in the first embodiment of the present invention, nor is it formed as a direct extension of the conducting pads of the sensor as it is in the first embodiment of the present invention. Furthermore, unlike the second embodiment of the present invention, the heat dissipation element of Ibaraki et al. is placed on the surface of the sensor overcoat and is not incorporated within the sensor overcoat itself. It is, therefore, the purpose of the present invention to provide two simple and efficient methods whereby the heat dissipation properties of a read/write element can be significantly improved.

SUMMARY OF THE INVENTION

[0015] A first object of this invention is to provide a method for forming a magnetic read/write head and slider assembly having improved heat spreading and dissipation characteristics when compared to magnetic read/write heads and slider assemblies of the prior art.

[0016] A second object of the present invention is to provide a method for forming such a magnetic read/write head and slider assembly having improved heat spreading and dissipation characteristics, wherein said method of formation is simple and efficient and requires only a slight variation in the present method of forming such a head and slider.

[0017] A third object of this invention is to provide a magnetic read/write head and slider assembly having significantly improved heat spreading and dissipation characteristics.

[0018] A fourth object of this invention is to provide a read/write head and slider assembly wherein there will be no protrusion of head elements and overcoat relative to the air bearing surface of the head during normal operating conditions.

[0019] In accord with the objects of this invention and as a first embodiment thereof, there is provided a magnetic read/write head and slider assembly and a method for forming such a magnetic read/write head and slider assembly, wherein one of the electrically conductive pads that connects the internal current carrying leads of the head to the external circuitry is enlarged and extended over a substantial portion of the bottom of the slider (the trailing end surface) so that it covers and thermally contacts the portion of the overcoat that is above the head structure. Since said pad is typically fabricated of gold or other material that is both electrically and thermally highly conductive, much more thermally conductive than the overcoat material, the enlargement and extension of the pad provides significant additional heat spreading (reduction of sharp temperature gradients) and heat dissipation for the head and slider assembly. Since the external electrical leads connected to the pads offer additional heat dissipation, the effect is magnified and rendered even more advantageous.

[0020] As a second embodiment of this invention there is provided a heat sink mechanism that consists of a highly thermally conductive layer formed within the overcoat layer rather than on top of it as in the first embodiment. There are several alternatives that meet the objectives of this second embodiment, a first alternative being a heat sink layer that is formed over the upper pole piece of the write element and possibly separated from it by an insulating layer and either completely or partially extending over the inductive coils of the element and a second alternative wherein the heat sink layer covers the upper or lower surface of the lower pole piece of the write element. In either alternative, the material of which the heat sink is formed must have a higher thermal conductivity than the material which it excludes and replaces.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The objects, features and advantages of the present invention are understood within the context of the Description of the Preferred Embodiments, as set forth below. The Description of the Preferred Embodiments is understood within the context of the accompanying figures, wherein:

[0022]FIG. 1 is a schematic drawing of a cross-section of a magnetic read/write slider/head assembly that is representative of both the prior art and the present invention. For purposes of discussion, the plane of the cross-section is the x-y plane and x denotes the slider length direction.

[0023]FIG. 2 is a schematic drawing of the top surface configuration (trailing end of the slider) of a read write head fabricated in accord with the prior art. The plane of this drawing is the y-z plane relative to the drawing of FIG. 1. The trailing end surface displayed represents the surface of attachment of the slider/head assembly to the external wires along the actuator arm assembly.

[0024]FIGS. 3 and 4 are the graphed results of simulations carried out to show the temperature profile in the x-direction (FIG. 3) and the z-direction (FIG. 4) across a head of the prior art during normal operating conditions.

[0025]FIGS. 5 and 6 show graphed simulation results of the protrusion profiles of the head and overcoat regions corresponding to the temperature profiles of FIGS. 3 and 4 respectively.

[0026]FIG. 7 is analogous to FIG. 2, being a schematic view of the rear surface of a slider/head assembly whose connective pads are formed in accord with the methods of the present invention.

[0027]FIGS. 8 and 9 are, respectively, graphical representations of simulated temperature profiles in the slider length direction (x) and the slider width direction (z) for a slider fabricated in accord with the first preferred embodiment of the present invention. Each graph also shows the corresponding graphs for a reference slider fabricated in accord with the prior art.

[0028]FIGS. 10 and 11 are graphical representations of simulations of the thermal protrusion profiles corresponding, respectively, to the temperature profiles of FIGS. 8 and 9.

[0029]FIGS. 12A, B & C are schematic representations of two overhead (A), (B) and a side cross-sectional view (C) of a stitched pole type of write head incorporating two versions of a heat sink layer, one of which (A) that covers an entire upper surface of the upper pole yoke and the induction coils, the other of which (B) partially covers the upper pole yoke and induction coils, both being in accord with the second preferred embodiment of the invention.

[0030]FIG. 13 is a schematic representations of a side cross-sectional view of a stitched pole type of read head incorporating a heat sink layer that is formed on the upper surface of the lower pole piece, but not impinging on the gap region. The layer could also be formed on the lower surface of the lower pole piece. Either position would be in accord with the objects of the second preferred embodiment.

[0031]FIG. 14 is a graphical representation of the protrusion modeling of a heat sink of particular material composition and dimension, formed in accord with the schematic illustration of FIGS. 12A & C.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] The first preferred embodiment of the present invention provides an efficient and effective method for materially improving the heat dissipation and heat spreading characteristics and eliminating associated thermal protrusion problems of a merged magnetic read/write head and slider assembly by the enlargement of at least one of its current lead connecting pads. The efficacy of this method has been substantiated by simulations that compare heads fabricated according to the method of the invention with heads fabricated according to methods of the prior art.

[0033] Referring first to FIG. 1, there is shown a schematic, not-to-scale, cross-sectional diagram of a read/write head and slider assembly typical of the prior art, mounted on an actuator arm assembly at its trailing end surface. For the purposes of description, the cross-sectional plane is the x-y plane as shown in the diagram and the z-axis can be taken as coming out of the plane. The air bearing surface (ABS) of the head is denoted as (1). The head comprises a magnetoresistive read sensor element (8) formed contiguously with the lower magnetic pole piece (4) of an inductive magnetic write element which also serves as an upper shield for the read element. The upper pole piece is of the write element is (6). Between the upper and lower pole pieces can be seen the cross-sections of the energizing coil turns (5) which are encased in a protective medium (12). The read element is shielded below by (3). The pole pieces come together to form a write gap (7). A protective overcoat surrounds the entire formation (2). Typically four internal conductive leads (three not shown) would emerge from the head and terminate at connecting pads (only (10) is shown) on the trailing end surface of the slider assembly, two leads to provide energizing current to the coil and two leads to provide sensing current to the read head. Only one such internal conducting lead is indicated (9) and that lead is shown terminating in a conductive pad (10) that emerges at the trailing end of the head (14). In actuality, there would be four such pads, one attached to each of the internal leads, said pads providing the electrically conducting contact to the external circuitry. The slider assembly connects to the actuating arm (30) along surface (15) to complete the fabrication, with the pads (10) providing the means for connecting the (partially drawn) internal conducting leads (9) to external leads (13).

[0034] Referring next to FIG. 2, there is shown a schematic drawing of the surface of the trailing end of the read head, which is shown only as (14) in FIG. 1. The plane of the surface is the z-y plane. The drawing shows the trailing end surface (14) and all four of the conductive pads (10), (18), (16), (20). The pads connect by conducting lines (19), (9) beneath the surface (drawn as dashed lines) to the write coil leads and read element (neither shown) within the head (12), which is also beneath the surface and drawn as dashed. Referring next to FIG. 3, there is shown a graph of temperature (° C.) vs. distance (in microns) in the x-direction or slider length direction (see FIG. 1) resulting from a simulation of a read/write head of the prior art under operating conditions. The x=0 position corresponds to the bottom of the head, x=20 microns locates the top of the head and the region from x=20 microns to x=35 microns encompasses the overcoat. As can be seen from the graph, there is a sharp temperature peak near the overcoat boundary which is a result of the poor heat conduction through the overcoat material.

[0035] Referring next to FIG. 4, there is shown the temperature distribution of FIG. 3 as measured (by the simulation) in the z-direction (slider width). Once again, the temperature is peaked in the read head region.

[0036] Referring next to FIGS. 5 and 6, there is shown graphical evidence of head and overcoat protrusion (in nanometers) produced by the temperature distributions in FIGS. 3 and 4. In this particular case, the maximum protrusion occurs in the overcoat region.

[0037] Referring next to FIG. 7, there is shown a schematic drawing of the trailing surface of a slider fabricated according to a first preferred embodiment of the method of the present invention. This figure is to be compared to the illustration in FIG. 2, which shows the corresponding surface of a prior art slider. As can be seen in FIG. 7, pad (16′), which corresponds to pad (16) of FIG. 2, has been substantially extended (17) to cover the head region (12) (beneath (17)). Said pad is formed of a metal, such as Au, Ag, Al or Cu, which is both electrically and thermally conductive. In practice, any good heat and electrical conductor that can be efficiently and easily plated on the overcoat material can be used. In the present embodiment, Au is used because it is easily plated on the alumina overcoat and because the remaining conductive pads are also Au. Heat generated within the head region beneath (17) is, therefore, efficiently transferred to the pad extension by conduction, is spread through both the pad and associated external wiring that it is attached to and is dissipated thereby. Given the purpose served by the pad extension, it should be seen that the shape of the extension is not critical, but it should be of sufficient area to completely cover that region of the trailing end surface that is directly over the read head, while not being of so large an area as to interfere with the other connecting pads. In the present embodiment, the Au pad extension, which is plated through a mask, is approximately square in shape and approximately 200 microns by 200 microns in size (area) and approximately between 4 and 5 microns in thickness.

[0038] Referring next to FIGS. 8 and 9, there are shown simulated temperature profiles along the x (FIG. 8) and z (FIG. 9) directions for a slider fabricated according to the first preferred embodiment of the method of the present invention (10) and for a slider fabricated according to the prior art (20). The prior art slider profiles are the same as those in FIGS. 3 and 4.

[0039] Referring next to FIGS. 10 and 11, there are shown the protrusion profiles corresponding to the temperature profiles in FIGS. 8 and 9. Once again, (10) indicates the invention and (20) indicates the prior art. The significant reduction in protrusion is readily apparent.

[0040] Referring to FIGS. 12A, B and C, there are shown two overhead views and one side cross-sectional view of a heat sink formed on a stitched pole type of writer in accord with a second preferred embodiment of the present invention. FIG. 12C is a side cross-sectional view in which can be seen the plane of the air-bearing surface (ABS) (2), which plane contains an intersection with the write gap (4) formed by the space between the upper pole tip (6) and the lower pole piece (8). The pole tip (6) is stitched to the pole yoke (10), over which is formed the heat sink layer (14) in accord with the second preferred embodiment of the invention. The heat sink layer, which is formed of a material with a thermal conductivity superior to that of surrounding materials (insulating overcoat materials) and which acts to conduct heat away from sensitive regions of the sensor and to dissipate it, may be separated from the actual upper surface of the pole yoke by a spacer layer (12), which is typically a layer of electrically non-conductive material. Suitable materials with high thermal conductivities include Cu, Ag, Au, Ni, Al, Ta, W and their alloys. It is also recognized that the material of which the heat sink layer is formed may be electrically conducting material or may be magnetic material, but in the latter case said material will serve only as a heat conducting and dissipating material. In either case, the spacer layer may be necessary to provide electrical or chemical isolation between the materials of the heat sink and the pole yoke. A preferred configuration would consist of a copper heat sink between 0.25 and 10 microns thick, separated from the magnetic material of the pole yoke by an electrically insulating alumina spacer layer between 0 and 10 microns thick. Also shown in the figure are the inductive coils (16) for providing the magnetic writing field and the insulating and protective overcoat material (18) which is also preferably alumina. As can be seen in the upper views provided by FIGS. 12A and 12B, the size and shape of the heat sink layer (14) may vary appreciably, but it should extend at least substantially over the pole yoke (10) and the coils (16). Although the heat sink layer is here pictured schematically as being rectangular in shape, it is recognized that the actual shape may be dictated by the topology of the write head. In FIG. 12A, the layer is shown as covering virtually the entire yoke and coil region, whereas in 12B it is shown to have a more restrictive area. It should also be recognized that the dimensions of the heat sink layer will depend on the dimensions of the write element, the thermal conductivity of the layer material and the amount of thermal energy to be dissipated.

[0041] Referring next to FIG. 13, there is shown a schematic cross-sectional view of a write element similar in all respects to the element in FIG. 12C with the exception of the position of the heat sink layer (30), which is here shown to cover a portion of the upper surface (31) of the lower pole piece (8). It is understood that it may be advantageous to form the heat sink layer as a double layer with a lower spacer layer of electrically insulating material. Although it is not shown in the figure, an alternative position, equally capable of satisfying the objectives of the invention, would be on the lower surface (32) of the pole piece.

[0042] Referring finally to FIG. 14, there is shown a graphical representation of the results of modeling the protrusion of a writer surface relative to the ABS plane vs. distance measured from the writer substrate for writers with (1) and without (2) a heat sink layer. The heat sink layer in this case is a 1.5 micron thick copper layer covering a yoke of length 18 microns and separated from it by an alumina spacer of approximately 0.3 microns thickness in accord with the configuration of FIG. 12. The coil layers dissipate a power of approximately 50 mW. The upper pole tip begins at approximately 5 microns from the substrate and its trailing edge is approximately 35 microns from the substrate.

[0043] As is understood by a person skilled in the art, the preferred embodiment of the present invention is illustrative of the present invention rather than limiting of the present invention. Revisions and modifications may be made to methods, materials, structures and dimensions employed in the present method of fabricating a magnetic read/write head and slider assembly with improved heat dissipation and thermal protrusion properties, while still providing a read/write head and slider assembly with improved heat dissipation and thermal protrusion properties, in accord with the spirit and scope of the present invention as defined by the appended claims. 

What is claimed is:
 1. A method for fabricating a magnetic read/write head and slider assembly having improved heat spreading and heat dissipation characteristics and reduced thermal protrusion comprising: providing a read/write head and slider assembly wherein the write element portion of said read/write head comprises at least a lower magnetic pole piece, an upper pole tip and yoke assembly and an inductive coil positioned between said pole piece and yoke; forming a heat sink layer over the upper surface of the yoke, said layer being in thermal contact with the yoke; forming an insulating overcoat over the assembly.
 2. The method of claim 1 wherein the heat sink layer covers the entire yoke and extends over the entire area of the inductive coil beneath it.
 3. The method of claim 1 wherein the heat sink layer covers a portion of the yoke and extends over a portion of the area of the inductive coil beneath it.
 4. The method of claim 1 wherein the material of which the heat sink layer is formed is a material having thermal conductivity which is higher than that of surrounding and contiguous materials.
 5. The method of claim 4 wherein the material of which the heat sink layer is formed is selected from the group consisting of electrically conducting materials and magnetic materials.
 6. The method of claim 5 wherein the material of which the heat sink layer is formed is selected from the group of materials with high thermal conductivities consisting of Cu, Au, Ag, Ni, Al, Ta, W, alloys thereof and combinations thereof.
 7. The method of claim 1 wherein the heat sink layer is a double layer, comprising a first layer which is an electrically insulating spacer layer and a second layer selected from the group of electrically conducting and magnetic materials and wherein the electrically insulating layer is in contact with the upper surface of the yoke.
 8. The method of claim 7 wherein the second layer is a layer of Cu formed to a thickness of between approximately 0.25 and 10 microns.
 9. The method of claim 7 wherein the first layer is a layer of alumina formed to a thickness of between approximately 0 and 10 microns.
 10. The method of claim 1 wherein the overcoat layer is a layer of alumina.
 11. A method for fabricating a magnetic read/write head and slider assembly having improved heat spreading and heat dissipation characteristics and reduced thermal protrusion comprising: providing a read/write head and slider assembly wherein the write element portion of said read/write head comprises at least a lower magnetic pole piece, an upper pole tip and yoke assembly and an inductive coil positioned between said pole piece and yoke; forming a heat sink layer in thermal contact with a portion of a surface of the lower magnetic pole piece; forming an insulating overcoat over the assembly.
 12. The method of claim 11 wherein the heat sink layer covers a portion of the upper surface of the lower magnetic pole piece and extends laterally beneath a substantial portion of the inductive coil.
 13. The method of claim 11 wherein the heat sink layer covers a portion of the lower surface of the lower magnetic pole piece and extends laterally beneath a substantial portion of the inductive coil.
 14. The method of claim 11 wherein the material of which the heat sink layer is formed is a material having thermal conductivity which is higher than that of surrounding and contiguous materials.
 15. The method of claim 14 wherein the material of which the heat sink layer is formed is selected from the group consisting of electrically conducting materials and magnetic materials.
 16. The method of claim 15 wherein the material of which the heat sink layer is formed is selected from the group of materials with high thermal conductivities consisting of Cu, Au, Ag, Ni, Al, Ta, W, alloys thereof and combinations thereof.
 17. The method of claim 11 wherein the heat sink layer is a double layer, comprising a first layer which is an electrically insulating spacer layer and a second layer selected from the group of electrically conducting and magnetic materials and wherein the electrically insulating layer is in contact with the upper surface of the yoke.
 18. The method of claim 17 wherein the second layer is a layer of Cu formed to a thickness of between approximately 0.25 and 10 microns.
 19. The method of claim 17 wherein the first layer is a layer of alumina formed to a thickness of between approximately 0 and 10 microns.
 20. The method of claim 11 wherein the overcoat layer is a layer of alumina.
 21. A magnetic read/write head and slider assembly having improved heat spreading and heat dissipation characteristics and reduced thermal protrusion comprising: a read/write head and slider assembly wherein the write element portion of said read/write head comprises at least a lower magnetic pole piece, an upper pole tip and yoke assembly and an inductive coil positioned between said lower magnetic pole piece and yoke; a heat sink layer formed over the upper surface of the yoke, said layer being in thermal contact with the yoke; and an insulating overcoat formed over the assembly.
 22. The assembly of claim 21 wherein the heat sink layer covers the entire yoke and extends over the entire area of the inductive coil beneath it.
 23. The assembly of claim 21 wherein the heat sink layer covers a portion of the yoke and extends over a portion of the area of the inductive coil beneath it.
 24. The assembly of claim 21 wherein the material of which the heat sink layer is formed is a material having thermal conductivity which is higher than that of surrounding and contiguous materials.
 25. The assembly of claim 21 wherein the material of which the heat sink layer is formed is selected from the group consisting of electrically conducting materials and magnetic materials.
 26. The assembly of claim 25 wherein the material of which the heat sink layer is formed is selected from the group of materials with high thermal conductivities consisting of Cu, Au, Ag, Ni, Al, Ta, W, alloys thereof and combinations thereof.
 27. The assembly of claim 21 wherein the heat sink layer is a double layer, comprising a first layer which is an electrically insulating spacer layer and a second layer selected from the group of electrically conducting and magnetic materials and wherein the electrically insulating layer is in contact with the upper surface of the yoke.
 28. The assembly of claim 27 wherein the second layer is a layer of Cu formed to a thickness of between approximately 0.25 and 10 microns.
 29. The assembly of claim 27 wherein the first layer is a layer of alumina formed to a thickness of between approximately 0 and 10 microns.
 30. The method of claim 1 wherein the overcoat layer is a layer of alumina.
 31. A magnetic read/write head and slider assembly having improved heat spreading and heat dissipation characteristics and reduced thermal protrusion comprising: a read/write head and slider assembly wherein the write element portion of said read/write head comprises at least a lower magnetic pole piece, an upper pole tip and yoke assembly and an inductive coil positioned between said lower magnetic pole piece and yoke; a heat sink layer formed on a surface of the lower magnetic pole piece; and an insulating overcoat encapsulating the assembly.
 32. The assembly of claim 31 wherein the heat sink layer covers a portion of the upper surface of the lower magnetic pole piece and extends laterally beneath a substantial portion of the inductive coil.
 33. The assembly of claim 31 wherein the heat sink layer covers a portion of the lower surface of the lower magnetic pole piece and extends laterally beneath a substantial portion of the inductive coil.
 34. The assembly of claim 31 wherein the material of which the heat sink layer is formed is a material having thermal conductivity which is higher than that of surrounding and contiguous materials.
 35. The assembly of claim 34 wherein the material of which the heat sink layer is formed is selected from the group consisting of electrically conducting materials and magnetic materials.
 36. The assembly of claim 34 wherein the material of which the heat sink layer is formed is selected from the group of materials with high thermal conductivities consisting of Cu, Au, Ag, Ni, Al, Ta, W, alloys thereof and combinations thereof.
 37. The assembly of claim 34 wherein the heat sink layer is a double layer, comprising a first layer which is an electrically insulating spacer layer and a second layer selected from the group of electrically conducting and magnetic materials and wherein the electrically insulating layer is in contact with the upper surface of the yoke.
 38. The assembly of claim 37 wherein the second layer is a layer of Cu formed to a thickness of between approximately 0.25 and 10 microns.
 39. The assembly of claim 37 wherein the first layer is a layer of alumina formed to a thickness of between approximately 0 and 10 microns. 